Reversing motor system for a laundry appliance

ABSTRACT

The motor of a laundry appliance is selectively driven in either a unidirectional or an alternating rotary manner by a single phase induction motor to rotate a clothes basket during a fluid extraction operation and to oscillate an agitation device during a laundry agitation period. The motor is provided with a pair of stator windings connected in opposite polarity sense, one of these windings being connected to an alternating voltage source for continuously receiving an alternating voltage wave while the other winding is selectively and/or cyclically connected across the voltage input terminals for a very brief period to reverse the motor. The motor with an electronic control circuit forms the basis of a simplified drive system for an automatic laundry appliance.

United States Patent Karklys et al.

[1 1 3,688,170 1 Aug. 29, 1972 [54] REVERSING MOTOR SYSTEM FOR A LAUNDRYAPPLIANCE [72] Inventors: Joseph Karklys, St. Joseph; Stephen A. Becker,Benton Harbor, Mich.

[73] Assignee: Whirlpool Corporation, Benton Harbor, Mich.

[22] Filed: April 16, 1971 211 App]. No.: 134,580

[52] US. Cl ..318/207 A, 318/221 R, 318/225 R, 318/227, 318/289 [51]Int. Cl. ..H02p 1/42 [58] Field or Search...3l8/207 A, 207 R, 221 R,225, 318/227, 289

[56] References Cited UNITED STATES PATENTS 9/1970 Wolf ..3l8/227 X Metz..3l8/207 R Primary Examiner-Gene Z. Rubinson Attorney1-lill, Sherman,Meroni, Gross & Simpson [57] ABSTRACT The motor of a laundry applianceis selectively driven in either a unidirectional or an alternatingrotary manner by a single phase induction motor to rotate a clothesbasket during a fluid extraction operation and to oscillate an agitationdevice during a laundry agitation period. The motor is provided with apair of stator windings connected in opposite polarity sense, one ofthese windings being connected to an alternating voltage source forcontinuously receiving an altemating voltage wave while the otherwinding is selectively and/or cyclically connected across the voltageinput terminals for a very brief period to reverse the motor. The motorwith an electronic control circuit forms the basis of a simplified drivesystem for an automatic laundry appliance.

18 Claims, 8 DrawingFigures Pope ...'.....31s/207 R REVERSING MOTORSYSTEM FOR A LAUNDRY APPLIANCE BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to drive systems for automaticwashers, and in particular to a modified induction motor and associatedcontrol circuitry and drive system components which form an automaticwasher drive mechanism.

2. Description of the Prior Art Heretofore, drive systems for automaticlaundry appliances which utilize an alternating rotary type of agitationgenerally have included transmissions which convert unidirectionalmotion created by a motor to the desired oscillatory motion.Alternatively, DC motors have been used in various direct drive systemswhich suffer from a requirement for relatively elaborate controlcircuitry to effect the desired agitation and spin operations. Inaddition, the art recognizes the utilization of an energy storage devicebetween the drive source and agitator in an automatic washer.

Generally, the various techniques for reversing single phase motors havea number of disadvantages when the techniques are applied to laundryappliance drive systems which require frequent periodic reversal. Thesedisadvantages include: overheating of the motor due to operation forlong periods at low efficiency and low self-ventilating speeds; poorswitch life; high cost due to requirements for large capacitors,switches, complex feedback circuitry and additional ventilating means;and difficulty in providing a drive system which has good agitatoraction as well as good spin characteristics.

SUMMARY OF THE INVENTION It is an object of the invention to provide animproved drive system for an automatic washer utilizing a reversinginduction motor in a direct driving relationship with an agitator.

It is also an object of the invention to provide an improved method forreversing an induction motor.

It is a further object of the invention to provide a modified inductionmotor and a control circuit for effect-ing very rapid reversal of themotor in a controlled cyclic manner.

As set forth in a copending application of Nystuen entitled InductionMotor Structure and Method of Operation, Ser. No. 134,579 and filed onan even date herewith, a modified induction motor construction andmethod of operating the modified motor are provided to .effectcontrolled reversal of the motor in an extremely rapid and reliablemanner. The foregoing and other objectives are realized through practiceof the instant invention which utilizes this type of motor constructionand an additional method of energizing the motor along with anappropriate control circuit to provide a drive system for an automaticlaundry appliance.

According to the invention a motor is provided with a rotor and a pairof stator windings, each of the stator windings taking a general formwhich is typical of conventional stator windings for induction motors.The two stator windings are connected in opposite polarity sense withrespect to each other and, contrary to the switching of applied voltagefrom one winding to the other as done in the aforementioned Nystuenapplication, one of the windings is connected to an alternating voltagepower source to continuously receive an alternating voltage wave, whilethe other winding is selectvely and cyclically connected across thevoltage source at or near time spaced zero crossings of the alternatingvoltage wave. Such energization of the motor creates a very rapidreversal of the direction of rotation of the motor, and the motor isperiodically reversed in this manner to provide the alternating drivefor the agitator of an automatic washing apparatus.

The motor may be connected to the agitator by means of a torsion springwhich is intended to absorb mechanical transients and promotes a smoothagitating operation.

A unijunction transistor relaxation oscillator is included in a controlcircuit connected to the motor, and

conduction of the unijunction transistor is utilized to develop a gatingpulse for a controlled conduction device which serves as a switch toconnect and disconnect the second stator winding from the voltage inputterminals at appropriate times.

DESCRIPTION OF THE DRAWING Other objects, features and advantages of theinven-' tion, its organization, construction and operation will becomeapparent and the invention will best be understood by reference to thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic elevational view of a laundry appliance which mayadvantageously employ a reversing motor system constructed in accordancewith the principles of the present invention;

FIGS. 2a-2d are graphical illustrations of several voltage wave fomrswhich may be applied to the stator windings to effect a rapid reversalof the motor;

FIGS. 3a and 3b are graphical illustrations of motor torque andsynchronous speed with respect to time illustrating the speed of motorreversal according to the invention; and

FIG. 4 is a schematic circuit diagram of a motor having two statorwindings and the associated control circuit according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A complete description of awinding arrangement and method by which an induction motor may berapidly reversed utilizing a phenomenon associated tion of washingliquid between the tub 11 and the interior of the spin basket 13.

Also mounted within the tub l1 and further within the interior of thespin basket 13 is an agitator 15. The agitator l5 and the spin basket 13are driven by a drive motor 16 which is coupled thereto by way of apulley 17, a belt 18, a pulley 19 and a drive shaft 20. The spin basket13 and the agitator 15 may be secured for common movement, or a clutchmechanism (not shown) may be provided as is well known in the art todrivingly engage the spin basket 13 and the agitator drive shaft 20.

The agitator 15 may be resiliently coupled to the agitator drive shaft20 as illustrated by means of a pair of torsion springs 21 and 22. Thesprings may be housed in an upper portion of the agitator l and coupledto this portion of the agitator and to the upper portion of the agitatordrive shaft 20. One of the springs 21 and 22 couples motion to theagitator when the drive shaft is rotating in a first direction and theother of springs 21 and 22 couples motion to the agitator when the driveshaft 20 is rotating in the opposite direction. Different types ofsprings or other resilient driving connections may be used to couple thedrive shaft 20 to the agitator 15 to ease the dynamic torsional loadingof the motor 16 during its cyclic reversals.

The drive motor 16 has a first winding connected across an alternatingvoltage power source 45 and is operated in a unidirectional or in anoscillator mode by means of a control circuit 24 which is efiective toapply voltage pulses to a second winding of the motor at or near zerocrossings of the applied voltage. The net effect of a properlysynchronized voltage pulse from the control circuit 24 is to create anegative torque pulse of large magnitude and brief duration. The impulsecreated by the negative torque pulse is sufiicient to overcome theinertia of the rotor and the driven load to provide an extremely rapidreversal of the motor.

The control circuit 24 is operative only during the agitation portion ofa washing cycle in accordance with a signal supplied via a lead 25 by anappliance timer 26. The timer 26 may be of the conventionalelectromechanical type in which a series of switch contacts aresequentially operated by a set of rotatably driven cams. Such timers arewell known in the art, and the timer 26 effectively controls the variousmachine operations including spin, as indicated by a lead 27 to themotor 16. The lead 27 may serve to energize an additional winding, ahigh speed winding, of the motor 16 to achieve a high spin speed duringthe extract portion of a washing cycle.

As set forth above and in the aforementioned Nystuen application,reversal of polarity of the voltage applied to an induction motor willproduce a rapid reversal of the motor rotor if care is taken that thepolarity reversal occurs in the vicinity of zero crossings of thevoltage. Due to a lagging power factor in motor operation, the necessaryswitching points occur at times when the current is at or near itsmaximum valve. Therefore, high voltages which may be damaging to solidstate switches are likely to be generated due to the amount of energystored in the inherent inductance of the system. In order toadvantageously utilize solid state switching without the fear ofdetrimental effects of such high voltages, the induction motor may beprovided with two windings, both located on the same axis and connectedin opposite polarity sense to each other. A rapid reversal of the motormay be effected by simply energizing one of the stator windingscontinuously in the normal fashion and applying a voltage pulse to thesecond winding at a zero crossing point of the applied voltage. It hasbeen found that a rapid motor reversal can be obtained by energizing thesecond winding for 1/2 cycle, 3/2 cycle, or 5/2 cycle of the appliedvoltage. These modes of energization are illustrated in FIG. 2, themotor reversal being initiated at 28. The inertia of the rotor andmachine load, usually are important in the selection of the most optimumof the aforementioned modes for fast reversal.

Energizing both stator windings for extended periods does not enhancethe motor reversal and, in fact, this may result in stalling and anexcessive current draw. It has also been found that energizing bothstator windings for a period comprising an even number of half cyclesdoes not enhance the motor reversal, and in factunder appropriatecircumstances such energization may preclude reliable reversal. This isdue to the fact that after the first half cycle of energization, eachsuccessive half cycle which is of opposite polarityhas an opposingeffect on the transients which effect the reversal. Therefore, it ispreferable to energize the motor windings for a period comprising an oddnumber of half cycles, thereby insuring that the number of half cyclesaiding the initial half cycle will be greater than the number of halfcycles opposing it, and that the last half cycle will be of the samepolarity as the initial half cycle.

Generally, within the limitations dictated by the environment of adomestic laundry appliance, energization of the second stator windingfor 1/2 cycle or 3/2 cycle of the applied alternating voltage has beenfound most desirable.

FIG. 3a illustrates the nature of the torque pulse which is developedwithin the motor 16 when the windings are energized by one of themethods of FIGS. 2a-2d. The torque pulse illustrated at 29 alwaysopposes the previous direction of motor rotation, and is of largemagnitude and short duration. The attendant rapid motor reversal isdepicted by the lower curve of FIG. 3b, and as illustrated the motor canalmost immediately achieve synchronous speed in the opposite direction,typically within approximately milliseconds.

FIG. 4 illustrates the motor 16 having two stator windings 30 and 31 ofthe type described in connection with a control circuit 24 for effectinga periodic or cyclic reversal of the motor. The control circuit 24 iseconomical and operates directly 45) a conventional alternating currentinput line L1, L2 (source 45() and eliminates the necessity for anyadditional power supplies. The control circuit 24 employs a unijunctiontransistor connected in a relaxation oscillator configuration for timingthe reversal pulses; however, other means, as for example digital 60Hcountdown, could be utilized for the same purpose. In addition, aposition sensing device for initiating motor reversal could also beemployed when synchronized to the positive half cycle of the input linevoltage.

More specifically, the circuit illustrated in FIG. 4 comprises a pair ofstator windings 30, 31 for providing the excitation field of the motor16. The first winding 30 is connected across the alternating voltageinput terminals L1, L2 and the second winding 31 is connected in serieswith a controlled conduction device, here illustrated a siliconcontrolled rectifier 32, the series combination being connected acrossthe input terminals L1, L2.

A relaxation oscillator 33 is provided for controlling the conduction ofthe controlled conduction device 32. The relaxation oscillator 33includes a resistor 34, a diode 35 and a capacitor 36 connected inseries across the input terminals L1, L2 for deriving a bias potentialat conductor 37 by charging of the capacitor 36 through the diode 35 andthe resistor 34. The direct current potential on conductor 37 isutilized for charging a capacitor 39 through a resistor 38 to providethe firing potential at the emitter of a unijunction transistor 40. Theunijunction transistor 40 has one base thereof connected by way of aresistor 41 to the conductor 37 and the DC potential thereat, and theother base thereof connected to the input terminal L2 by way of aresistor 42.

The resistor 42 is employed to develop a gating pulse thereacross uponconduction of the unijunction transistor .40, which gating pulse isapplied to a gate electrode 43 of the controlled conduction device 32 torender that device conductive and connect the second winding 31 acrossthe input terminals L1, L2.

The RC time constant of the resistor 38 and the capacitor 39 determinesthe periodic firing of the unijunction transistor 40 and accordingly theperiodic application of line voltage to the second stator winding 31. Asis well understood by those skilled in the art, once the SCR 32 isenergized by means of a pulse on its gate electrode 43, current willcontinue to flow through winding 31 and through the SCR 32 until themagnitude of the current drops substantially to zero, at which time theSCR will shut off and prevent further current flow through winding 31.Thus, it is seen that winding 31 can be energized only during positivehalf cycles of the AC voltage.

The periodic firing of the unijunction transistor 36 as determined bythe resistor 38 and the capacitor 39 is synchronized to voltage zerocrossings preceding positive half cycles of the AC line voltage by thesupply voltage ripple. Depending upon the values selected for resistor38 and capacitor 39, the time between timings of transistor 36 maycomprise numerous half cycles of the AC line voltage. Suchsynchronization to the zero crossing points of the AC voltage waveformis important if reliable and repeatable motor reversals are to beobtained.

The lead 25 from the electromechanical timer referred to earlier is seenas connected to the junctionof the resistor 38, the capacitor 39, andthe emitter lead 44 of the unijunction transistor 40. This enables theemitter of the unijunction transistor to be shorted to power supply leadL2 by means of an appropriate timer contact (not shown), therebystopping operation of the relaxation oscillator 33 and preventing theperiodic energization of SCR 32 and stator winding 31. Thus, theperiodic reversal of motor 16 can be halted as desired to perform otherportions of a washing cycle.

It should be understood that although the present control circuit isdesigned to energize the second stator winding 31 only during positivehalf cycles of the applied voltage, as illustrated by of FIG. 2b,energizing this winding during only the negative half cycles of theapplied voltage will also effect similar rapid reversal of the motor.Further, it should be understood that ener gizing the winding 31 forboth positive and negative half cycles of the applied voltage, asillustrated in the FIGS. 2c and 2d, will result in reversal of themotor,

although the present control circuit is not designed to operate in thismanner. An explanation of why those modes of energizing the winding 31also produces a rapid reversal can be found in the aforementionedNystuen application Ser. No. 134,579

The apparatus disclosed herein provides a simple and economical drivingsystem for a laundry appliance which operates equally well in aunidirectional rotational mode and in an oscillatory mode. Further, thesystem eliminates the necessity for complex feedback networks andadditional cooling and ventilating apparatus previously required inprior art reversible motor systems in that the mechanical transients areshort lived and reversal is almost instantaneous so that motor speed issufiiciently high to prevent overheating and to provide conventionalself-ventilating action.

While we have described our invention by reference to a specificillustrative embodiment thereof, changes and modifications of theinvention may become apparent to those skilled in the art and it is tobe understood that we wish to include within the patent warranted hereonall such changes and modifications as may reasonably and properly beincluded within the scope of our invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A motor reversing circuit comprising: input terminals for receivingan alternating voltage wave having cyclic zero crossover points; arotor; first and second stator windings inductively coupled to saidrotor and wound in opposite polarity sense to each other andrespectively connected across said input terminals; and reversing meansincluding switching means serially interposed in the connection betweensaid second winding and one of said input terminals, and switch controlmeans connected across said input terminals and connected to saidswitching means for actuating said switching means in response to and atselected zero crossover points to efiect controlled reversal of saidrotor.

2. A motor reversing circuit, comprising: input terminals for receivingan alternating voltage wave having cyclic zero crossover points; arotor; first and second stator windings inductively coupled to saidrotor and wound in opposite polarity sense to each other andrespectively connected across said input terminals; and reversing meansincluding switching means serially interposed in the connection betweensaid second winding and one of said input terminals, and switch controlmeans interconnected between said input terminals and connected to saidswitching means for actuating said switching means to effect controlledreversal of said rotor, wherein said switch control means includes arelaxation oscillator circuit connected to said switching means.

3. A motor reversing circuit according to claim 1, wherein saidswitching means includes a semi-conductor switch connected in circuit,with said second wind ing and having a gate electrode connected to saidswitch control means.

4. A motor reversing circuit, comprising: input terminals for receivingan alternating voltage wave having cyclic zero crossover points; firstand second stator windings inductively coupled to said rotor and woundin opposite polarity sense to each other and respectively connectedacross said input terminals; and reversing means including switchingmeans serially interposed in the connection between said second windingand one of said input tenninals, and switch control means interconnectedbetween said input terminals and connected to said switching means foractuating said switching means to effect controlled reversal of saidrotor, wherein said switching means includes a semi-conductor switchconnected in circuit with said second winding and having a gateelectrode connected to said switch control means, wherein said switchcontrol means includes a unijunction transistor having an emitter and apair of bases, first circuit means including a diode and a firstcapacitor connected in series across said input terminals so as todevelop a bias potential for said transistor, second circuit meansincluding an RC circuit connected across said first capacitor to developthe firing potential of said transistor in response to the directcurrent potential derived across said first capacitor, and a resistanceconnected in circuit with one of said bases and connected to saidswitching means for developing a switch operating pulse upon conductionof said transistor.

5. A motor reversing circuit according to claim 4, comprising meansconnected to said RC circuit and operable to inhibit the development ofthe firing potential for providing unidirectional rotation of saidrotor.

6. A motor circuit for a laundry appliance having a movable partcomprising: alternating voltage input terminals for receiving analternating voltage wave of positive and negative polarity; a firstwinding connected across said input terminals; a second winding; a rotorinductively coupled to said first and second windings and connected tothe movable part of said laundry appliance; switch means having acontrol terminal, said switch means and said second winding connected inseries across said input terminals with said second winding in anopposite polarity sense relative said first winding; and circuit meansconnected to said input terminals and to said control terminal tocyclically close said switch means during predetermined time-spaced halfcycles of the alternating voltage wave to effect cyclic reversals ofdirection of rotation of said rotor and said movable part of saidlaundry appliance.

7. A motor circuit for a laundry appliance according to claim 6, furtherincluding means for inhibiting the cyclic operation of said switch meansto efiect unidirectional rotation of said rotor and said movable part.

8. A motor reversing circuit according to claim 6, wherein said circuitmeans includes a unijunction transistor having an emitter and a pair ofbases, first circuit means including a diode and a first capacitorconnected in series across said input terminals to provide a biaspotential for said transistor, second circuit means including an RCcircuit connected across said first capacitor to develop the firingpotential for said transistor in response to the direct currentpotential derived across said first capacitor, and a resistanceconnected in circuit with one of said bases and connected to saidswitching means for developing a switch operating pulse upon conductionof said transistor.

9. A laundry appliance comprising: means defining a laundry treatmentzone for receiving laundry including a rotatable member; a motorincluding a rotor connected to said rotatable member, and a pair offield windings inductively coupled to said rotor; a pair of inputterminals for receiving an alternating voltage wave, said inputterminals connected to one of said windings and connectable to the otherof said windings in an opposite polarity sense relative said onewinding; and reversing means connected to said input terminals and tosaid other winding for periodically connecting said other winding tosaid input terminals for at least one half cycle of the alternating waveto provide a reversing torque to periodically reverse the direction ofrotation of said rotor and rotatable member for agitating the laundry insaid treatment zone.

10. A laundry appliance according to claim 9,

wherein said reversing means includes a control terminal, and saidappliance includes a timer circuit connected between said inputterminals and said control terminal for controlling the initiation andduration of operation of said reversing means. I

11. A motor reversing circuit comprising: alternating voltage inputterminals for receiving an alternating voltage wave of positive andnegative polarity; a motor including a first stator winding connectedtosaid input terminals for constant energization, a second statorwinding disposed in opposite polarity sense to said first stator windingfor connection across said input terminals, and a rotor inductivelycoupled to said first and second windings; and reversing means forreversing the direction of rotation of said rotor, said reversing meansincluding switch means connected in circuit with said input terminalsand said second winding and having a control terminal, and switchcontrol means connected to said input terminals and synchronized withthe zero crossings of the alternating wave and operable to cyclicallyoperate said switch means at a frequency less than that of thealternating wave to cyclically reverse the direction of rotation of saidrotor.

12. A motor reversing circuit according to claim 11,

wherein said switch control means includes a relaxation oscillatorcircuit connected to said switch means.

13. A motor reversing circuit according to claim 11, wherein saidswitching means includes a semi-conductor switch connected in circuitwith said second windings and having a gate electrode connected to saidswitch control means.

14. A motor reversing circuit according to claim 11, wherein said switchcontrol means includes a unijunction transistor having an emitter and apair of bases, first circuit means including a diode and a firstcapacitor connected in series across said input terminals to apply abias potential to said transistor, second circuit means including an RCcircuit connected across said first capacitor to develop the firingpotential for said transistor in response to the direct currentpotential derived across said first capacitor, and a resistanceconnected in circuit with one of said bases and connected to saidswitching means for developing a switch operating pulse upon conductionof said transistor.

15. A motor reversing circuit according to claim 11, wherein said switchcontrol means includes means operable to close said switch means forsubstantially one-half cycle of the alternating wave.

16. A method of cyclically reversing the direction of rotation of therotor of a single phase induction motor having first and secondoppositely wound field windings, comprising the steps of: continuouslyapplying an alternating voltage wave of positive and negative polarityacross said first field winding; and periodically applying one-halfcycle of the alternating voltage wave to said second field windingsimultaneously with the ap plication of the same half cycle voltage tosaid first winding.

17. The method of cyclically reversing the direction of rotation of asingle phase induction motor having first and second oppositely woundfield windings, comprising the steps of: continuously applying analternating voltage of positive and negative polarity across the step ofgenerating is further defined as including the step of synchronizing thegeneration of motor reversal signals with zero voltage points of thealternating voltage.

1. A motor reversing circuit comprising: input terminals for receivingan alternating voltage wave having cyclic zero crossover points; arotor; first and second stator windings inductively coupled to saidrotor and wound in opposite polarity sense to each other andrespectively connected across said input terminals; and reversing meansincluding switching means serially interposed in the connection betweensaid second winding and one of said input terminals, and switch controlmeans connected across said input terminals and connected to saidswitching means for actuating said switching means in response to and atselected zero crossover points to effect controlled reversal of saidrotor.
 2. A motor reversing circuit, comprising: input terminals forreceiving an alternating voltage wave having cyclic zero crossoverpoints; a rotor; first and second stator windings inductively coupled tosaid rotor and wound in opposite polarity sense to each other andrespectively connected across said input terminals; and reversing meansincluding switching means serially interposed in the connection betweensaid second winding and one of said input terminals, and switch controlmeans interconnected between said input terminals and connected to saidswitching means for actuating said switching means to effect controlledreversal of said rotor, wherein said switch control means includes arelaxation oscillator circuit connected to said switching means.
 3. Amotor reversing circuit according to claim 1, wherein said switchingmeans includes a semi-conductor switch connected in circuit, with saidsecond winding and having a gate electrode connected to said switchcontrol means.
 4. A motor reversing circuit, comprising: input terminalsfor receiving an alternating voltage wave having cyclic zero crossoverpoints; first and second stator windings inductively coupled to saidrotor and wound in opposite polarity sense to each other andrespectively connected across said input terminals; and reversing meansincluding switching means serially interposed in the connection betweensaid second winding and one of said input terminals, and switch controlmeans interconnected between said input terminals and connected to saidswitching means for actuating said switching means to effect controlledreversal of said rotor, wherein said switching means includes asemi-conductor switch connected in circuit with said second winding andhaving a gate electrode connected to said switch control means, whereinsaid switch control means includes a unijunction transistor having anemitter and a pair of bases, first circuit means including a diode and afirst capacitor connected in series across said input terminals so as todevelop a bias potential for said transistor, second circuit meansincluding an RC circuit connected across said first capacitor to developthe firing potential of said transistor in response to the directcurrent potential derived across said first capacitor, and a resistanceconnected in circuit with one of said bases and connected to saidswitching means for developing a switch operating pulse upon conductionof said transistor.
 5. A motor reversing circuit according to claim 4,comprising means connected to said RC circuit and operable to inhibitthe development of the firing potential for providing unidirectionalrotation of said rotor.
 6. A motor circuit for a laundry appliancehaving a movable part comprising: alternating voltage input terminalsfor receiving an alternating voltage wave of positive and negativepolarity; a first winding connected across said input terminals; asecond winding; a rotor inductively coupled to said first and secondwindings and connected to the movable part of said laundry appliance;switch means having a control terminal, said switch means and saidsecond winding connected in series across said input terminals with saidsecond winding in an opposite polarity sense relative said firstwinding; and circuit means connected to said input terminals and to saidcontrol terminal to cyclically close said switch means duringpredetermined time-spaced half cycles of the alternating voltage wave toeffect cyclic reversals of direction of rotation of said rotor and saidmovable part of said laundry appliance.
 7. A motor circuit for a laundryappliance according to claim 6, further including means for inhibitingthe cyclic operation of said switch means to effect unidirectionalrotation of said rotor and said movable part.
 8. A motor reversingcircuit according to claim 6, wherein said circuit means includes aunijunction transistor having an emitter and a pair of bases, firstcircuit means including a diode and a first capacitor connected insEries across said input terminals to provide a bias potential for saidtransistor, second circuit means including an RC circuit connectedacross said first capacitor to develop the firing potential for saidtransistor in response to the direct current potential derived acrosssaid first capacitor, and a resistance connected in circuit with one ofsaid bases and connected to said switching means for developing a switchoperating pulse upon conduction of said transistor.
 9. A laundryappliance comprising: means defining a laundry treatment zone forreceiving laundry including a rotatable member; a motor including arotor connected to said rotatable member, and a pair of field windingsinductively coupled to said rotor; a pair of input terminals forreceiving an alternating voltage wave, said input terminals connected toone of said windings and connectable to the other of said windings in anopposite polarity sense relative said one winding; and reversing meansconnected to said input terminals and to said other winding forperiodically connecting said other winding to said input terminals forat least one half cycle of the alternating wave to provide a reversingtorque to periodically reverse the direction of rotation of said rotorand rotatable member for agitating the laundry in said treatment zone.10. A laundry appliance according to claim 9, wherein said reversingmeans includes a control terminal, and said appliance includes a timercircuit connected between said input terminals and said control terminalfor controlling the initiation and duration of operation of saidreversing means.
 11. A motor reversing circuit comprising: alternatingvoltage input terminals for receiving an alternating voltage wave ofpositive and negative polarity; a motor including a first stator windingconnected to said input terminals for constant energization, a secondstator winding disposed in opposite polarity sense to said first statorwinding for connection across said input terminals, and a rotorinductively coupled to said first and second windings; and reversingmeans for reversing the direction of rotation of said rotor, saidreversing means including switch means connected in circuit with saidinput terminals and said second winding and having a control terminal,and switch control means connected to said input terminals andsynchronized with the zero crossings of the alternating wave andoperable to cyclically operate said switch means at a frequency lessthan that of the alternating wave to cyclically reverse the direction ofrotation of said rotor.
 12. A motor reversing circuit according to claim11, wherein said switch control means includes a relaxation oscillatorcircuit connected to said switch means.
 13. A motor reversing circuitaccording to claim 11, wherein said switching means includes asemi-conductor switch connected in circuit with said second windings andhaving a gate electrode connected to said switch control means.
 14. Amotor reversing circuit according to claim 11, wherein said switchcontrol means includes a unijunction transistor having an emitter and apair of bases, first circuit means including a diode and a firstcapacitor connected in series across said input terminals to apply abias potential to said transistor, second circuit means including an RCcircuit connected across said first capacitor to develop the firingpotential for said transistor in response to the direct currentpotential derived across said first capacitor, and a resistanceconnected in circuit with one of said bases and connected to saidswitching means for developing a switch operating pulse upon conductionof said transistor.
 15. A motor reversing circuit according to claim 11,wherein said switch control means includes means operable to close saidswitch means for substantially one-half cycle of the alternating wave.16. A method of cyclically reversing the direction of rotation of therotor of a single phase induction motor having first and secondoppositely wouNd field windings, comprising the steps of: continuouslyapplying an alternating voltage wave of positive and negative polarityacross said first field winding; and periodically applying one-halfcycle of the alternating voltage wave to said second field windingsimultaneously with the application of the same half cycle voltage tosaid first winding.
 17. The method of cyclically reversing the directionof rotation of a single phase induction motor having first and secondoppositely wound field windings, comprising the steps of: continuouslyapplying an alternating voltage of positive and negative polarity acrossthe first field winding; generating a periodic series of motor reversalsignals; and periodically applying at least one-half cycle of thealternating voltage wave to the second winding simultaneously with theapplication of the same to the first winding in response to each of saidmotor reversal signals.
 18. The method according to claim 17, whereinthe step of generating is further defined as including the step ofsynchronizing the generation of motor reversal signals with zero voltagepoints of the alternating voltage.